The present invention relates to grain elevators and more particularly to a chute system to deliver grain to a silo.
At the present time grain elevators are commonly used to receive and store grain such as wheat. The grain is lifted by a conveyor belt or a pneumatic tube to a door near the top of the grain silo where it is dumped into the silo. The silo is generally a large cylindrical building and may be typically 150 feet high and 60 feet in diameter. The grain is mixed with dust and typically the amount of dust may be from 3 percent to 6 percent of the mixture.
When the grain is dumped into the silo, it falls through air and some of the dust becomes separated from the falling grain, since the dust is lighter. The dust may form a dusty atmosphere, which is highly explosive. There have been numerous reported incidents of grain elevator explosions and fires. The delivery of grain into the grain silo is considered a dangerous period and care is taken to avoid sparks which would ignite an explosive atmosphere that may be found in the silo. To prevent build-up of such an explosive atmosphere, some silos have been provided with a large exhaust fan, for example, rated at 150 HP, which helps exhaust the dusty atmosphere from the silo. Such exhaust fans are relatively expensive to install and operate and may not completely solve the problem of preventing the build-up of an explosive atmosphere in the silo.
The patent literature contains many examples of grain chutes and chutes for other types of products. In U.S. Pat. No. 3,887,503 entitled "Gravity Chute Systems", a chute for soiled laundry or solid waste is intended to prevent compaction at the bottom and comprises a series of riser conduit sections. U.S. Pat. No. 3,797,625 entitled "Silo Chute With Separate Discharge Tube" discloses a chute, outside the silo, to discharge ensilage and has a vertical series of normally closed doors. In U.S. Pat. No. 4,066,158 entitled "Chute Construction" a security storage chamber for mail bags utilizes a collapsible chute. In U.S. Pat. No. 3,961,693 entitled "Inverted Silo Chutes Having Swingable Side Wall Panels" a bowed closable discharge chute is inside the silo. In U.S. Pat. No. 1,779,412 entitled "Coal Filling Chute" the chute has internal baffles. In U.S. Pat. No. 2,750,021 entitled "Distributor For Grain And The Like" an endless chain carries a camming device which opens doors in sequence. In U.S. Pat. No. 3,931,877 entitled "Material Diverter Structure" a tubular member within the chute cooperates with a carriage mounted diverter. U.S. Pat. No. 728,626 entitled "Conveyor" shows a package conveyor in the form of a spiral chute. U.S. Pat. No. 803,944 entitled "Conveying Apparatus" relates to bulky packages (sacks) and the loading of vessels and shows a chute having a plurality of doors and diverter baffles.
In addition, the non-patent literature contains references to the problems caused by the dust mixed with grain. An article in the July 8, 1982 issue of the Wall Street Journal states that grain dust explosions have killed more than 400 workers since 1960 and 108 workers since 1977. Another article, Dec. 12, 1983, in the Wall Street Journal discusses proposed Labor Department standards for grain elevators which would limit the floor dust to 1/8-inch thick or require clean-up after shift or require pneumatic dust control systems.
Flour mill dust (diameter 15 .mu.microns or 15/1000 mm) is a mechanical dispersoid in a gas (atmosphere). It is considerably smaller and lighter than the grain particles. The use of mechanical dust separation using filters, centrifugal cyclones, electrostatic precipitators and elongated fabric bags is known from conventional chemical engineering texts.